The present invention generally relates to radio communications and, more particularly, to lensed multi-beam antennas utilized in cellular communications systems.
Cellular communications systems are well known in the art. In a cellular communications system, a geographic area is divided into a series of regions that are referred to as “cells,” and each cell is served by a base station. The base station may include one or more antennas that are configured to provide two-way radio frequency (“RF”) communications with mobile subscribers that are geographically positioned within the cells served by the base station. In many cases, each base station provides service to multiple “sectors,” and each of a plurality of antennas will provide coverage for a respective one of the sectors. Typically, the sector antennas are mounted on a tower or other raised structure, with the radiation beam(s) that are generated by each antenna directed outwardly to serve the respective sector.
A common wireless communications network plan involves a base station serving three hexagonal shaped cells using three base station antennas. This is often referred to as a three sector configuration. In a three sector configuration, each base station antenna serves a 120° sector. Typically, a 65° azimuth Half Power Beamwidth (HPBW) antenna provides coverage for a 120° sector. Three of these 120° sectors provide 360° coverage. Other sectorization schemes may also be employed. For example, six, nine, and twelve sector configurations are also used. Six sector sites may involve six directional base station antennas, each having a 33° azimuth HPBW antenna serving a 60° sector. In other proposed solutions, a single, multi-column array may be driven by a feed network to produce two or more beams from a single phased array antenna. For example, if multi-column array antennas are used that each generate two beams, then only three antennas may be required for a six sector configuration. Antennas that generate multiple beams are disclosed, for example, in U.S. Patent Publication No. 2011/0205119, which is incorporated herein by reference.
Increasing the number of sectors increases system capacity because each antenna can service a smaller area and therefore provide higher antenna gain throughout the sector. However, dividing a coverage area into smaller sectors has drawbacks because antennas covering narrow sectors generally have more radiating elements that are spaced wider apart than are the radiating elements of antennas covering wider sectors. For example, a typical 33° azimuth HPBW antenna is generally twice as wide as a typical 65° azimuth HPBW antenna. Thus, cost, space and tower loading requirements increase as a cell is divided into a greater number of sectors.